This application claims priority to an application entitled xe2x80x9cDevice and Method for Processing Radio Link Protocol in Mobile Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Jun. 13, 1998 and assigned Serial No. 98-22216, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to a mobile communication system and in particular, to a device and method for processing a radio link protocol in a CDMA communication system. Specifically, the present invention relates to a device and method for processing a radio link protocol for packet data communication in a variable rate environment in a CDMA communication system.
2. Description of the Related Art
A code division multiple access (CDMA) mobile communication system is based on the IS-95 standard which mainly supports a voice service. In the near future, mobile communication systems will be based on the IMT-2000 standard which supports both voice service and high-speed data transfer service. For example, the IMT-2000 standard can support a high-quality voice service, a moving picture service, an Internet search service, etc. In the IS-95 CDMA mobile communication system which mainly supports the voice service, the maximum data rate is 9.6 Kbps or 14.4 Kbps. In the IMT-2000 CDMA communication system, a possible maximum data rate of 2 Mbps is attainable. Hence, data which can be transmitted within a unit time can be transmitted approximately 256 times faster using the IMT-2000 standard than the IS-95 standard for a CDMA mobile communication system.
The CDMA mobile communication system solves a data loss problem which frequently occurs in a radio environment which uses a radio link protocol (RLP). For the radio link protocol, a frame having a length of 20 ms is used. The frame is typically transmitted at a data rate of 9.6 Kbps or 14.4 Kbps. The 20 ms RLP frames are assigned sequence numbers so that a data frame which is lost during transmission in the radio environment may be retransmitted. The sequence numbers used in the radio link protocol during data frame transmission are composed of 8 bits, so that the radio link protocol can support a maximum of 256 frames.
In the case where the data rate increases and becomes greater than an existing data rate during retransmission of the radio link protocol, the frame to be retransmitted is transmitted together with another frame. Accordingly, it is possible to transmit the frames more effectively at the higher data rate. However, in the case where the data rate decreases and becomes lower than the existing data rate during retransmission of the radio link protocol, the frame to be retransmitted should be segmented, prior to transmission, into several frames to be suitable for a low transmission data rate.
In the latter case, the frame can be segmented into a maximum of three sub-frames. In this case, a receiving party reassembles the three sub frames into the original frame.
However, as indicated above, the IMT-2000 standard supports a maximum data rate of 2 Mbps, which is much greater than the maximum data rate of 9.6 Kbps or 14.4 Kbps supported in the radio link protocol. Hence, it is difficult to apply the existing radio link protocol having the low data rate to the IMT-2000 standard. Furthermore, to support various data rates, the frame segmentation process should be separately designated for the various complex situations.
It is, therefore, an object of the present invention to provide a device and method for effectively supporting a radio link protocol even in the case where a mobile station and a base station of a mobile communication system connected to each other via a radio channel experiences a change in data rate.
It is another object of the present invention to provide a device and method for retransmitting data lost during transmission for protecting the integrity of the transmitted data, especially in the case where a mobile station performing packet data communication with a base station of a mobile communication system experiences a change in data rate with respect to a connected radio channel during data transmission.
It is further another object of the present invention to provide a device and method for effectively retransmitting lost data by proposing a termination frame not to generate a data-less frame in a mobile communication system.
To achieve the above objects, a method is provided for generating sequence numbers for an RLP frame in a mobile communication system. The method includes the steps of generating a sequence number tree having a plurality of nodes each associated with frame information and a data rate; upon receipt of a sequence number request from an RLP controller, reading, at an RLP sequence number generator, frame information for a designated node from the sequence number tree and providing the read frame information to the RLP controller; and upon receipt of the frame information in response to the sequence number request, transmitting and receiving a frame at the RLP controller.